The present invention relates to foamed treatment fluids and, more particularly, to foaming and foam stabilizing surfactant mixtures for use in treatment fluids and associated methods.
Foamed treatment fluids may be used in a variety of subterranean treatments, such as drilling operations, well bore cleanup operations, hydraulic fracturing, fracture acidizing, sand control treatments, and the like. As used herein, a “treatment fluid” refers to any fluid used in subterranean treatments for a desired function and/or a desired purpose and does not imply any particular action by the fluid. A foamed treatment fluid may be prepared by mixing an aqueous fluid containing a foaming and foam stabilizing surfactant mixture with a gas (such as air, nitrogen, carbon dioxide, or combinations thereof). Generally, the foaming and foam stabilizing surfactant mixture facilitates the foaming of the aqueous fluid and also may stabilize the resultant foamed fluid formed therewith. Foamed treatment fluids may effectively carry particulates and also may require a smaller amount of gelling agent, reducing the amount of residue left in the subterranean formation by the gelling agent. Additionally, foamed treatment fluids have low fluid loss properties, potentially reducing or removing the need for a fluid loss control additive. Furthermore, foaming a treatment fluid generally reduces the water requirement, thereby minimizing problems associated with clay swelling.
Hydraulic fracturing is a process commonly used to increase the flow of desirable fluids, such as oil and gas, from a portion of a subterranean formation. Hydraulic fracturing operations generally involve introducing a foamed treatment fluid (e.g., a foamed fracturing fluid) into a subterranean formation at or above a pressure sufficient to create or enhance one or more fractures in the formation. Enhancing a fracture includes enlarging a pre-existing fracture in the formation. The foamed treatment fluid may comprise particulates, often referred to as “proppant particulates,” that are deposited in the fractures. The proppant particulates function to prevent the fractures from fully closing upon the release of pressure, forming conductive channels through which fluids may flow to (or from) the well bore. After the fracturing operation is complete, the pressure on the well bore is released. This allows the gas in the foamed treatment fluid to expand and, with this expansion, the energized foamed treatment fluid flows from the formation, flows into the well bore, and exits the well bore at the surface.
Foamed treatments fluids also may be used in sand control treatments, such as gravel packing. In gravel pack treatments, the foamed treatment fluid suspends gravel particulates for delivery to a desired area in a well bore, e.g., near unconsolidated or weakly consolidated formation zones, to form a gravel pack that enhances sand control. One common type of gravel packing operation involves placing a sand control screen in the well bore and packing the annulus between the screen and the well bore with the gravel particulates of a specific size designed to prevent the passage of formation sand. The gravel particulates act, inter alia, to prevent the formation particulates from occluding the screen or migrating with the produced hydrocarbons, and the screen acts, inter alia, to prevent the gravel particulates from entering the production tubing. Once the gravel pack is substantially in place, the pressure on the well bore is released. This allows the gas in the foamed treatment fluid to expand and, with this expansion, the foamed treatment fluid flows from the formation, into the well bore, and exits the well bore at the surface.
While foamed treatment fluids have been used previously, the use of certain conventional foaming and foam stabilizing surfactant mixtures has been problematic. For example, foamed treatment fluids, that contain certain conventional foaming and foam stabilizing surfactant mixtures (e.g., alcohol ether sulfates by themselves) in general, tend to destabilize when contacted by small quantities of oil. Accordingly, when used in hydrocarbon-bearing formations, these foamed treatment fluids may prematurely destabilize resulting in an undesired loss of viscosity. This premature loss of viscosity may be problematic, for example, the proppant or gravel particulates may not be deposited in the desired location in the formation.